Cylinder deactivation is used for improving fuel efficiency in engines. Cylinder deactivation cuts off one-half of the available cylinders by deactivating valve lift in those cylinders such that the cylinders remain closed after a combustion cycle of the engine, and the burnt gases remain trapped within the cylinder during deactivation.
The remaining active cylinders on an engine which has some of its cylinders deactivated through valve deactivation generally work at a higher specific load. This higher specific load along with the reduction in exhaust pulse frequency raises concerns over higher amplitude and corresponding increased exhaust noise. Conventional means for attenuating exhaust sound, such as mufflers having resonators therein, usually come with a detrimental higher exhaust back pressure. This higher exhaust back pressure works to diminish the improvements gained from deactivating cylinders.
Accordingly, a need exists to address the exhaust noise problem associated with cylinder deactivation.